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Revision as of 11:56, 22 February 2013 by Dragons flight (talk) (Update to allow for unnamed parameters. This is necessary because some string function need to preserve leading / trailing whitespace in order to work properly.)
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Documentation for this module may be created at Module:String/doc

local str = {}

function str.len( frame )
    return mw.ustring.len( frame.args.s )

function str.sub( frame )
    return mw.ustring.sub( frame.args.s, tonumber( frame.args.i ), tonumber( frame.args.j ) )

function str.sublength( frame )
    local i = tonumber( frame.args.i ) or 0
    local len = tonumber( frame.args.len )
    return mw.ustring.sub( frame.args.s, i + 1, len and ( i + len ) )

function str.match( frame )
    return mw.ustring.match( frame.args.s, frame.args.pattern, tonumber( frame.args.i ) )


This function duplicates the behavior of {{str_find}}, including all of its quirks.
This is provided in order to support existing templates, but is NOT RECOMMENDED for 
new code and templates.  New code is recommended to use the "find" function instead.

Returns the first index in "source" that is a match to "target".  Indexing is 1-based,
and the function returns -1 if the "target" string is not present in "source".

Important Note: If the "target" string is empty / missing, this function returns a
value of "1", which is generally unexpected behavior, and must be accounted for
function str.str_find( frame )
    local new_args = str._getParameters( frame.args, {'source', 'target'} );
    local source_str = new_args['source'] or '';
    local target_str = new_args['target'] or '';

if target_str == '' then
        return 1;
    local start = mw.ustring.find( source_str, target_str, 1, true )
    if start == nil then
        start = -1
    return start


This function allows one to search for a target string or pattern within another


    source: The string to search
    target: The string or pattern to find within source
    start: The index within the source string to start the search, defaults to 1
    plain: Boolean flag indicating that target should be understood as plain
        text and not as a Lua style regular expression, defaults to true

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the parameter.  In some circumstances this is desirable, in 
other cases one may want to preserve the whitespace.

This function returns the first index >= "start" where "target" can be found 
within "source".  Indices are 1-based.  If "target" is not found, then this 
function returns 0.  If either "source" or "target" are missing / empty, this
function also returns 0.

This function should be safe for UTF-8 strings.
function str.find( frame )
    local new_args = str._getParameters( frame.args, {'source', 'target', 'start', 'plain' } ); 
    local source_str = new_args['source'] or '';
    local pattern = new_args['target'] or '';
    local start_pos = tonumber(new_args['start']) or 1;
    local plain = new_args['plain'] or true;
    if source_str == '' or pattern == '' then
        return 0;
    if type( plain ) == 'string' then
        plain = plain:lower();
        if plain == 'false' or plain == 'no' or plain == '0' then
            plain = false;
            plain = true;

    local start = mw.ustring.find( source_str, pattern, start_pos, plain )
    if start == nil then
        start = 0
    return start

Helper function that populates the argument list given that user may need to use a mix of
named and unnamed parameters.  This is relevant because named parameters are not
identical to unnamed parameters due to string trimming, and when dealing with strings
we sometimes want to either preserve or remove that whitespace depending on the application.
function str._getParameters( frame_args, arg_list )
    local new_args = {};
    local index = 1;
    local value;
    for i,arg in ipairs( arg_list ) do
        value = frame_args[arg]
        if value == nil then
            value = frame_args[index];
            index = index + 1;
        new_args[arg] = value;
    return new_args;

return str